Description:
Abstract: The MSAR corrosion test loop was used to study the effect of VKE-shaped crevices on the corrosion resistance of Zircaloy under boiling heat-transfer condtions in both ammoniated and lithiated water at pH 10.5.

Description:
From AIAA/NSA/ASTM/IES 7th space simulation conference; Los Angeles, Calif11nia, USA (12 Nov 1973). In order to obtain steady state data on nucleate boiling heat transfer to liquid helium in a nearly zero gravity environment a rocket-borne experiment was designed, built and successfully flown. A description of the apparatus and flight is presented along with preliminary results. (auth)

Description:
Compact heat exchangers are becoming more attractive for applications in which energy conservation, space saving, and cost are important considerations. Applications exist in the process industries where phase-change heat transfer realizes more compact designs and improved performance compared to single-phase heat transfer. However, there have been only a few studies in the literature reporting on phase-change heat transfer and two-phase flow in compact heat exchangers, and validated design correlations are lacking. Recent data from experiments on flow boiling of refrigerants in small channels have led researchers to conclude that nucleation is the dominant heat transfer mechanism over a broad range of heat flux and wall superheats. Local heat transfer coefficients and overall two-phase pressure drops were measured for three different refrigerants with circular and non-circular channels in a range of pressures. This data base supports the nucleate boiling mechanism, and it was used to develop a new correlation for heat transfer in nucleate flow boiling. The correlation is based on the Rohsenow boiling model, introducing a confinement number defined by Kew and Cornwell. The new correlation predicts the experimental data for nucleate flow boiling of three refrigerants within {+-}15%.

Description:
The physical phenomenon of forced convective boiling is probably one of the most interesting and complex transport phenomena. It has been under study for more than two centuries. Simply stated, forced convective subcooled boiling involves a locally boiling fluid: (1) whose mean temperature is below its saturation temperature, and (2) that flows over a surface exposed uniformly or non-uniformly to a high heat flux (HHF). The objective of this work is to assess and/or improve the present ability to predict local axial heat transfer distributions in the subcooled flow boiling regime for the case of uniformly heated coolant channels. This requires an accurate and complete representation of the boiling curve up to the CHF. The present. results will be useful for both heat transfer research and industrial design applications. Future refinements may result in the application of the results to non-uniformly heated channels or other geometries, and other fluids. Several existing heat transfer models for uniformly heated channels were examined for: (1) accurate representation of the boiling curve, and (2) characterizing the local heat transfer coefficient under high heat flux (HHF) conditions. Comparisons with HHF data showed that major correlation modifications were needed in the subcooled partial nucleate boiling (SPNB) region. Since the slope of boiling curve in this region is important to assure continuity of the HHF trends into the fully developed boiling region and up to the critical heat flux, accurate characterization in the SPNB region is essential. Approximations for the asymptotic limits for the SPNB region have been obtained and have been used to develop an improved composite correlation. The developed correlation has been compared with 363 water data points. For the local heat transfer coefficient and wall temperature, the over-all percent standard deviations with respect to the data were 19% and 3%, respectively, for the high ...

Description:
>The effects of an ultrasonic field on the maximum nucleate heat flux that can be sustained by boiling water in a flow system are being investigated. Design and procurement of apparatus is underway. (M.C.G.)

Description:
An investigation was made to increase the basic knowledge of nucleate and film boiling heat transfer to fluids up to their critical pressures. An extensive literature survey of the subject indicated a scarcity of consistent data and an absence of proven methods for analysis. This situation led to the design and construction of experimental apparatus suitable for measuring rates of free convection heat transfer and associated temperature differences for fluid conditions up to 4000 psi and 800 deg F, with provision for visual observation. The apparatus incorporated a stainless steel system for containing the fluid. Ten-mil-diameter cylindrical and 1/8-in.-high vertical-plate platinum test sections were placed in the fluid inside a pressure vessel, 5 in. in inside diameter and 21 in. high. The pressure and temperature of the fluid envirorment were controlled by constant-volume heating of the fluid in the pressure vessel with the aid of seven zones of radiant guard heaters located between the external wall of the pressure vessel and the insulation. Each of these zones was controlled by a differential-thermocouple-sensed circuit that automatically kept the pressure vessel at a prescribed uniform temperature. Fluid pressure was measured with a deadweight tester and a 0-4000-psi Heise gauge. Fluid temperature was measured with a calibrated resistance thermometer and Mueller bridge, purchased specifically for that purpose. The heat flux in the test section was obtained from electrical measurements of the directcurrent power supplied for Joule heating. The temperature of the test section was measured by means of a resistance thermometer. The system was outgassed and filled under a vacuum with water that was deionized, degassed, and deionized again. The quality of the water was maintained during an experiment with the aid of a thermalsiphon deionizing loop which was connected to the system. The results were tabulated and plotted in terms of heat ...

Description:
An experimental apparatus was constructed to examine the heat-transfer characteristics of a sputtering front. In the present study, a heat source of sufficient intensity was located immediately below the sputtering front, which prevented its downward progress, thus permitting detailed measurements of steady-state surface temperatures throughout a sputtering front. A two-dimensional analytical model was developed to describe a stationary sputtering front where the wet-dry interface corresponds to a CHF phenomena and the dry zone is adiabatic. This model is nonlinear because of the temperature dependence of the heat-transfer coefficient in the wetted region and has yielded good agreement with data. A simplified one-dimensional approximation was developed which adequately describes these data. Finally, by means of a coordinate transformation and additional simplifying assumptions, this analysis was extended to analyze moving sputtering fronts, and reasonably good agreement with reported data was shown.

Description:
An analytical expression is presented which permits the prediction of the maximum nucleate heat flux in pool boiling of saturated or subcooled liquids. The numerical values of the empirical constants which appear in the Kutateladze and Borishanskii criteria for the burnout'' heat flux are derived from the theory. An analytical expression for the empirical function which appears in the correlation of Griffith is also derived. The hitherto unexplored features of transition boiling, i.e., the hydrodynamic instability, the well defined geometrical configuration and the frequency dependence are described, supported by experimental evidence, and used as the basis for the analytical work. The peak heat flux in transition boiling is shown to be limited by the combined effects of Taylor and Helmholtz instabilitiess whereas the minimum transitional heat flux is limited by the effect of Taylor instability ony. The analysis leads to the conclusion that because of the statistical nature of the ddsturbances and the bandwidth'' of the unstable wavelengths which govern the process, an inherent uncertainty exists in determining the exact value of the heat flux at burnout.'' The width of this uncertainty range is plus or minus 14%. The often noted poor reproducibility of experimental data on burnout'' can be inferred, therefore, from the analysis. The reason analytical attacks upon the burnout'' problem, based upon considerations of bubble agitation and other nucleate boiling characteristics, have not been successful is discussed. The literature has shown conclusively that the surface conddtions play the dominant role in determining the superheat accompanying a given heat flux. The analysis reveals, in addition, that even if the nucleating characteristics of the surface were known the problem could still not be solved from these considerations because the mechanism of the instability occurs in the fluid away from the surface. The extension of the analysis to flow systems ...

Description:
A study of nucleate boiling of subcooled water in forcedconvection source-vortex flow in small diameter horizontal tubes is described. A measured heat flux of ll,000,000 Btu/hr ft/sup 2/ was attained, a value 5 times greater than any previously reported for comparable conditions. (T.R.H.)

Description:
The results of a study to determine reliable heat transfer data for the design of a suitable heat exchanger for the Intermediate Scale Homogeneous Reactor are presented. Design studies of a vertical submerged-tube evaporator with nucleate boiling from the outer tube surfaces and of a vertical tube, forced-circulation evaporator are presented in detail. (M.P.G.)

Description:
In recent years, subooled nucleate boiling (SNB) has attrcted expanding research interest owing to the emergence of axial offset anomaly (AOA) or crud-induced power shigt (CIPS) in many operating US PWRs, which is an unexpected deviation in the core axial power distribution from the predicted power curves. Research indicates that the formation of the crud, which directly leads to AOA phenomena, results from the presence of the subcooled nucleate boiling, and is especially realted to bubble motion occurring in the core region.

Description:
The design and construction of the Boiling Nuclear Superheater (BONUS) Power Station at Punta Higuera on the seacoast at the westernmost tip of Puerto Rico are described. The reactor has an output of 17.5 Mw(e). This report will serve as a source of information for personnel engaged in management, evaluation, and training. (N.W.R.)

Description:
In this paper, we further investigate the hypothesis that the critical heat flux (CHF) occurs when some point on the heated surface reaches a high enough temperature that liquid can no longer contact that point, resulting in a gradual but continuous increase in the overall surface temperature. This hypothesis unifies the occurrence of the CHF and the quenching of hot surfaces by relating both to the same concept, i.e., the ability of a liquid to contact a hot surface. We use a two-dimensional transient conduction model to study the boiling phenomenon in the second transition region of saturated pool nucleate boiling on a horizontal surface. The heater surface is assumed to consist of two regions: a dry patch region formed as a result of complete evaporation of the thinner liquid macrolayers and a two-phase macrolayer region formed by numerous vapor stems penetrating relatively thick liquid macrolayers. The constitutive relations used to determine the stem-macrolayer configuration in the two-phase macrolayer region of the boiling surface were reevaluated for Gaertner's clean water and water-nickel/salt solution. 29 refs.

Description:
This study experimentally investigated the effect of hydrophobic and hydrophilic surfaces characteristics on nucleate boiling heat transfer performance for the application of direct immersion cooling of electronics. A dielectric liquid, HFE – 7100 was used as the working fluid in the saturated boiling tests. Twelve types of 1-cm2 copper heater samples, simulating high heat flux components, featured reference smooth copper surface, fully and patterned hydrophobic surface and fully and patterned hydrophilic surfaces. Hydrophobic samples were prepared by applying a thin Teflon coating following photolithography techniques, while the hydrophilic TiO2 thin films were made through a two step approach involving layer by layer self assembly and liquid phase deposition processes. Patterned surfaces had circular dots with sizes between 40 – 250 μm. Based on additional data, both hydrophobic and hydrophilic surfaces improved nucleate boiling performance that is evaluated in terms of boiling incipience, heat transfer coefficient and critical heat flux (CHF) level. The best results, considering the smooth copper surface as the reference, were achieved by the surfaces that have a mixture of hydrophobic/hydrophilic coatings, providing: (a) early transition to boiling regime and with eliminated temperature overshoot phenomena at boiling incipience, (b) up to 58.5% higher heat transfer coefficients, and (c) up to 47.4% higher CHF levels. The studied enhanced surfaces therefore demonstrated a practical surface modification method for heat transfer enhancement in immersion cooling applications.

Description:
This paper describes the use of a new test apparatus employing flow visualization via ultra-high-speed video and microscope optics to study microscale nucleate boiling in a small, rectangular, heated channel. The results presented are for water. Because of confinement effects produced by the channel cross section being of the same nominal size as the individual vapor bubbles nucleating at discrete wall sites, flow regimes and heat transfer mechanisms that occur in small channels are shown to be considerably different than those in large channels. Flow visualization data are presented depicting discrete bubble/bubble and bubble/wall interactions for moderate and high heat flux. Quantitative data are also presented on nucleate bubble growth behavior for a single nucleation site in the form of growth rates, bubble sizes, and frequency of generation in the presence and absence of a thin wall liquid layer. Mechanistic boiling behavior and trends are observed which support the use of this type of research as a powerful means to gain fundamental insights into why, under some conditions, nucleate boiling heat transfer coefficients are considerably larger in small channels than in large channels.

Description:
Experimental and analytical investigations to determine the effects of irregular heat flow through reactor channels on the operating conditions that cause burnout (departure from nucleate boiling) are being planned. Tubular specimens having four axial power shapes and annular specimens having five power shapes will be used, and an effort to correlate the experimental data with empirical and analytical models will be made. The experimental program will be conducted on a vertical test section in a closed loop through which water is circulated at a given rate. A 1.8Mw d-c power supply will heat the test section. (auth)

Description:
A significant number of current PWRs around the world are experiencing anomalous crud deposition in the sub-cooled region of the core, resulting in an axial power shift or Axial Offset Anomaly (AOA), a condition that continues to elude prediction of occurrence and thermal/neutronic performance. This creates an operational difficulty of not being able to accurately determine power safety margin. In some cases this condition has required power ''down rating'' by as much as thirty percent and the concomitant considerable loss of revenue for the utility. This study examines two aspects of the issue: thermal performance of crud layer and effect of sub-cooled nucleate boiling on the solute concentration and its influence on initiation of crud deposition/formation on fuel pin surface.

Description:
Development of an improved semimechanistic-based set of correlation parameters for nucleation-dominant flow-boiling heat transfer in small channels is described. Formulation of these parameters is on the basis of a recently published open-literature model for vapor bubble growth at a heated surface. This work is part of a program directed at obtaining an understanding of the physical mechanisms that influence boiling in compact heat exchangers through the use of high-speed video and microscope optics to characterize bubble nucleation, growth, and interaction with the confining walls of small heat transfer passages. The correlation parameters presented here represent the first step in the development of an improved boiling correlation for geometrically confined small-channel flows. In such flows, the nucleating bubbles can become nominally the same size as the channel cross section, thereby invalidating existing correlations that are based on large-channel data. Initial efforts to correlate small-channel-boiling data obtained at Argonne National Laboratory from nontransparent electrically heated metal tube tests appear promising.

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